Solid electrolytic capacitors (e.g., tantalum capacitors) have been a major contributor to the miniaturization of electronic circuits and have made possible the application of such circuits in extreme environments. Conventional solid electrolytic capacitors are often formed by pressing a metal powder (e.g., tantalum) around a metal lead wire, sintering the pressed part, anodizing the sintered anode, and thereafter applying a solid electrolyte. The part is then finished by applying a metal layer, which can act as a conductor, contact layer, or charge collector for the capacitor. A carbonaceous layer is typically disposed between the solid electrolyte and the metal layer to limit the contact between the metal layer and the solid electrolyte, which would otherwise increase the resistance of the capacitor. One problem, however, is that it is often difficult to achieve good adhesion between the carbonaceous layer and the solid electrolyte, which can also result in an increase in the resistance of the capacitor. Various attempts have been made to address this problem. U.S. Pat. No. 8,125,768 to Horacek, et al., for instance, describes the use of a polymeric outer layer that is disposed between the carbonaceous layer and the graphite layer to improve adhesion between the solid electrolyte and the carbonaceous layer. Unfortunately, this technique is still problematic in that achieving good adhesion between each of these layers can still be difficult, which can result in delamination of these layers from the capacitor body. Such delamination can increase the electrical series resistance (ESR) of the capacitor, which detrimentally affects the electrical performance of the capacitor.
As such, a need remains for a solid electrolytic capacitor where delamination between the solid electrolyte and the external layers of the solid electrolytic capacitor is minimized.